Pressure-sensing signal generator

ABSTRACT

Extremely sensitive apparatus for detecting effort of a patient to inhale and to produce a powerful output signal of very short duration in response for initiating action of a respirator, with means immunizing the apparatus against adverse temperature change effects, means for stabilizing operation of the apparatus, and means for varying the sensitivity of the apparatus to pressure differential.

11111111 ites 1e Inventor Gerald L. McConnell Riverside, Calili.

Appl. No. 865,919

Filed Oct. 13, 11969 Patented Oct. 5, 1971 Assignee Bourns, llnc.

missmtiisiisme slicmr tiisisimiron 5 Claims, 3 Drawing Figs.

11.8. C1 331/65, 128/142.2, 128/422, 324/61, 331/117 R, 331/174, 340/279lint. Q] A62b 7/04, GOln 27/22, H03b 5/12 Field 011 Search 331/65,

117, 174; 324/61; 328/];73/384; 340/279,421; 128/208, 140, 142.2, 145.5,145.8,422, DIG. 17

[56] lkeiercnces Cited UNITED STATES PATENTS 3,019,397 1/1962 Cosby331/65 3,153,205 10/1964 .lonesetal. 33l/65X 3,191,595 6/1965 Wilson128/1455 3,357,428 12/1967 Carlson 128/1458 Primary Examiner-Roy LakeAssistant Examiner-Siegfried H. Grimm AtmrneyFritz B. Peterson ABSTRACT:Extremely sensitive apparatus for detecting effort of a patient toinhale and to produce a powerful output signal of very short duration inresponse for initiating action of a respirator, with means immunizingthe apparatus against adverse temperature change effects, means forstabilizing operation of the apparatus, and means for varying thesensitivity of the apparatus to pressure differential.

PRESSURE-SENSING SIGNAL GENERATOR BRIEF SUMMARY OF THE INVENTION a.Background of the Invention In certain applications of pressure changesensing, it is imperative to very quickly and positively sense pressuredecrease below ambient or a determined level or value, and to generate asignal indicative of the change for use in or by an apparatus. Forexample, in respirator apparatus adapted for use in relief of hyalinemembrane syndrome and other breathing difficulties evidenced by neonatalinfants, it is of importance to sense very weak efforts to inhale by theinfant and to immediately aid the infant by supplying air or a specialmixture of gases under superambient pressure to the infant via nasalmask means, and to thereafter permit free exhalation by the infant at adetermined subsequent time. The effort to inhale causes a drop inpressure, however slight, at the nostril entrance; and this pressurechange has been utilized, by use of pressure change sensing means, toinitiate action of the respirator to supply or deliver an accuratelymeasured volume of air, oxygen enriched or otherwise, under regulatablepressure and at a regulatable speed, to the infant patient. Therespirator is so devised that following delivery of the air, valve meansare operated and exhaling is accomplished by natural contraction of thechest cavity of the patient. The same factors are noted in respect ofrespirator mechanisms employed for other than neonates. Heretoforevarious kinds of pressure transducers have been employed to provide anoutput for initiating actuation of respirator means, such transducersincluding pressuresensitive electric switches. Since the pressure sensoris most desirably situated as close as is practicable to the nostrils ofthe patient, whereby sensitivity may be maximized, and since switchmeans in proximity to a patient, and especially near to oxygen oroxygen-enriched air, are undesirable, designers of respiratory aidsystems have had to compromise between optimum sensitivity and attendantundesirable factors. One compromise has resulted in the use of sealedreed switch means operated by a pressure-sensitive means, locateddistant from the nasal mask and having a sensitivity much less than isdesirable. No fully satisfactory solution to the problem of providing anextremely sensitive safe means for rapidly initiating action of therespirator means incident to an effort to inhale by the patient has beenattained prior to advent of the present invention. Thus, it is a primeobject of the invention herein disclosed in a presently preferredexemplary form to obviate the noted disadvantages of prior art devicesof the indicated class; and it is a broad object of the invention toprovide improvements in means for initiating action ofrespiration-augmenting means. A more specific object is to provide anextremely sensitive, extremely fast-acting regulatable means forproducing a powerful signal indicative of an effort of a patient toinhale and which signal can be utilized to initiate action of othermeans such as a respirator. Other objects and advantages of the presentinvention are hereinafter stated or made evident in the appended claimsand disclosure of the preferred exemplary embodiment.

b. Brief Description of the Invention According to the invention,presence of electric switch means in proximity to the patient isavoided, and extreme sensitivity of sensor means is concurrentlyattained, by using electrical capacitor means, a movable plate orelectrode of which is disposed on a thin resilient membrane or diaphragmwhich in turn is exposed on one face to the ambient and on the other tothe interior of a passage closely communicating with the nasal passagesof the patient, as sensor means sensitive to any effort of the patientto inhale. The capacitive means is connected in the circuit of anelectronic oscillator and is effective to initiate oscillation of theoscillator incident to very slight change of capacitance as thediaphragm moves in response to very slight change in differentialpressure as the patient makes an effort to inhale. The oscillatorcircuit is so devised that commencement of oscillation results intransmission of an electric signal which is used to activate or toinitiate activation of means in the respirator system. The exemplarysystem comprising the oscillator circuit is further devised to beselfquenching, whereby the oscillator is quenched from oscillatory toquiescent status at the end of a brief interval of time (e.g., 5milliseconds) next following initiation of oscillation.

Thus, unless the capacitor means has returned to the neutral attitudeduring the signal generation period, the oscillator is again triggeredinto oscillation, generates another signal, and again quenches, andrepetitively does so until the capacitor means returns to the initialneutral attitude and capacitance value. The signal, in the form of anelectric wave, is integrated, preferably following wave shaping and/0ramplification in circuitry of the system, to produce an output signalfor transmission to and utilization in the respirator. In therespirator, arrival of the output signal is effective to set in motioncyclical means which then operates through one cycle during which ameasured volume of air is supplied under moderate superatmosphericpressure to the nasal mask on the patient over a regulatable period oftime which is followed by a period during which valve means are operatedand the patient exhales. The respirator is so devised that in one modeof operation the cyclical operation is automatically repeated and inanother mode of operation the cycle is again initiated by attemptedinspiration by the patient. An exemplary circuit according to thepresent invention permits variation of the sensitivity of the detectingmeans, whereby action is initiated only in response to subatmosphericpressure in the mask of any selected value in the range from 0.1 mm. to5.0 cm. of water column. Since the oscillator is set into oscillation asthe result of a very small movement of a diaphragm-supported capacitorelectrode, the circuit can be employed to detect a very small mechanicalmovement of a part connected to the electrode. The circuit is soarranged that capacitive means including the pressure-sensitivecapacitor means, herein termed the principal capacitor, are in shuntwith the oscillatory circuit of the oscillator, the capacitive meansfurther comprising a variable capacitor in the form of avoltage-variable capacitor whereby the effective value of the shuntcapacitance may be varied by varying the potential applied across thelater capacitor. The circuit preferably includes an amplifier whichprovides a strong output signal during oscillation of the oscillator;and a portion of the output signal is fed back via signal-delay means tothe voltage-variable capacitor to change the shunt capacitance to avalue that causes rapid decay and extinction or quenching of theoscillation of the oscillator after a determined period of time. Sincereturn of the capacitor to a. capacitance value at which oscillation isinitiated will not generally cause the oscil lator to stop oscillating,the feedback quenching of the oscillator permits of greatly increasingsensitivity of the signal generator to change of pressure at the movableportion of the principal capacitor. To enhance stability of operationand sensitivity, the active elements of the oscillator are temperaturestabilized by enclosing them in an oven that is maintained at atemperature somewhat above room temperature, e.g., at

The preferred voltage-variable capacitor is a voltage-sensitive diode;and the preferred active element of the oscillator is a field-effecttransistor. A trimming or adjusting capacitor is provided for initialadjustment of the oscillator. A preferred form and arrangement ofcomponents of an exemplary pressure-sensitive signal generator isdepicted in schematic form in connection with a known respirator in theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is a functional block diagram of an exemplary system according tothe invention;

FIG. 2 is a fragmentary sectional view of the exemplarypressure-sensitive capacitor comprised in the capacitive shunt connectedto the oscillator of the system; and

FIG. 3 is a detailed circuit diagram of the signal generator part of thesystem.

DETAILED DESCRIPTION OF THE INVENTION Referring f'ust to FIG. 2, thereis illustrated in section a pressure-sensitive capacitor device orsensor adaptable to delicately sense change of pressure from ambientatmospheric pressure to a lower value. The drawing is essentiallyschematic and to not specific scale. The sensor comprises means in theform of a box providing a chamber sealed at the peripheral juncturebetween the body 10b and cover 100 of the box. Disposed in body 10b is arigid stop device 12 formed of molded material. The stop and box body10b are bored to provide an opening for reception of a conduit 14 whichis supported by the body and communicates with the mentioned nose mask(not shown) which is per se not of the present invention and may be ofthe type illustrated in U.S. Pat. No. 3,357,428 or that illustrated inU.S. Pat. No. 1,206,045, for examples. The cover 100 is of insulationand is similarly bored to receive and support an conduit 16 which isopen to the ambient atmosphere. The box is preferably of circular planform, and has secured thereto at the interior periphery along thejuncture of the cover and body a thin resilient diaphragm 20. Thediaphragm overlies a centrally perforated circular metal electrode 18awhich is affixed to cover 10c and forms one electrode of a principalcapacitor herein denoted C1 in the circuit diagram. A second metal plate18b, complementary to plate 180 and which may be formed of a film ofmetal formed on the diaphragm, serves as a movable electrode ofcapacitor C1. Flexible conductors 22a and 22b, connected as indicated inthe drawings, serve as respective terminal connectors for the capacitorplates. An extension of cover 10c serves as a base for support of anenclosure 24 in which other components of the signal generator may behoused, as on a circuit board.

As is evident, when air exits from the chamber above diaphragm incidentupon an effort by the patient to inhale consequent reduction of pressurein conduit 14, the diaphragm will be forced to move in the directionaway from electrode 18a under the influence of the ambient air and itspressure in the chamber below the diaphragm. Thus the capacitance ofcapacitor C1 is lessened or decreased. The slight change in capacitanceis employed to initiate action of circuitry connected to capacitor C1 asshown in detail in FIG. 3 and in block diagram form in FIG. 1.

Referring to FIGS. 1 and 3, the capacitor unit comprisingpressure-sensitive capacitor C1 is connected to serve as the primarycontrol component, in shunt to an oscillator unit 40. The oscillatorunit, herein termed the oscillator in the interest of brevity, comprisestapped inductor L1, capacitor C2, resistor R1 and field-effecttransistor Q1, all connected as a Hartley oscillator. Closely regulatedor constant-potential DC power is supplied as from a battery B by way oflead Pl (negative) and ground (positive) as indicated. An oscillatortrimming unit 50 comprising variable capacitor C2 is connected as afeedback control in the oscillatory circuit of unit 40, as shown. Thusthe oscillator capacitance can be adjusted to a proper value to permitquenching and oscillation initiation as will presently be described.

A temperature-regulating unit 60 which comprises a heater Rx of thenegative resistance type such as is sold under the trade name KLIXON ishoused, together with temperaturesensitive components of the oscillator,in an insulated chamber or over I-l. Thus the unit 60, connected asshown and arranged as described, if effective when energized to raisethe temperature in which the temperature-sensitive components operate toa superambient value, e.g., 80 C.; and to maintain those components atthat constant temperature. Thus the oscillator is immunized againstadverse changes due to change in ambient temperature. The oven H is notshown in detail since it may be one of many kinds commercially availableor may be merely an insulated box. While in the drawing only thetransistor O1 is shown in the oven with the heater thermostat, it willbe understood that all components of the oscillator may be so housed.

When the oscillator is permitted to oscillate, it produces ahigh-frequency wave output. The circuit component values are such thatat each alternate half-cycle of the oscillation of the oscillatorycircuit the transistor Q1 quickly becomes saturated, whereby the outputto a coupling capacitor C4 is of substantially square wave form. Anexemplary oscillator frequency is 30 megahertz. Oscillation of theoscillator is pennitted only under special circumstances, and at othertimes is prevented by one or more actions of means presently described.

The square wave output signal passed through coupling capacitor C4 issubjected to rectification in a rectifier-integrator unit 70 whichcomprises diodes CR1 and CR2 and capacitor C5. The effect of the units70 is to supply to the gate of the transistor Q2 of an amplifier unit abias which causes or permits O2 to conduct during the duration of thesquare wave signal. Thus during that period a negative-going pulseappears on output signal lead P2. That output signal is transmitted toand utilized in the respirator unit 90. For example, the negative-goingpulse may be of the order of 5 milliseconds duration and may be used topull up a latching relay which initiates a cycle of action of therespirator. The respirator may be, for example, like or similar to thosedisclosed in U.S. Pat. Nos. 3,357,427 and 3,006,336; or similarbreathing-augmentor apparatuses.

Once a cycle of operations has commenced or been initiated by the outputsignal, air under pressure is forced into the mask and the pressure inthe chamber above the sensor diaphragm 20 (FIG. 2) increases to asuperambient value and the capacitance of capacitor C1 is increased atleast to its original value. However, that alone does not precludecontinued oscillation of the oscillator; hence means are provided forquenching the oscillator after oscillation has continued for a periodsufficient to insure relay pullup or other initiation of respiratoroperation. Such a period has herein been selected, for example, to be ofthe order of 5 milliseconds.

Amplifier transistor O2 is normally biased off by bias supplied by biasunit which comprises resistors R2 and R3 connected as indicated in FIG.3. Thus the amplifier unit will not provide an output signal until thebias provided by the bias unit 100 is overcome by the input signal fromthe unit 70. When an amplifier unit output signal is produced andtransmitted to the respirator unit 90, a quenching signal unit alsoreceives the amplifier output signal, via branch line P2. The quenchpulse unit comprises resistor R4. capacitor C6. transistor Q3, andconnections as shown. The negative-going pulse signal is effective tobuild up a charge on capacitor C6. via resistor R4 connected to line P2.When the potential across C6 reaches a determined value, transistor O3is biased to conduction. Transistor O3 is normally biased off by abiasing unit which comprises resistors RS and R6 and connections asindicated.

When the quenching signal unit transistor Q3 has thus been induced toconduct following an amplifier output signal duration of the notedcharacter, a current signal is produced which is transmitted via line P3and the resultant potential change is transmitted via radiofrequencychoke coil L2 to a voltage-sensitive capacitor CRX comprised in anoscillator quench unit 130. Capacitor CRX in series with auxiliarycapacitor C7 forms a variable capacitive shunt to ground for theoscillatory circuit of unit 40. The arrangement is such that withsubstantially no DC potential applied across capacitor CRX, theoscillator will commence oscillating as soon as the capacitance ofsensor capacitor C1 falls slightly incident to the patients attemptingto inhale. Thus, with the oscillator oscillating, a current signal isproduced by Q3 after about 5 milliseconds oscillation. The currentsignal produces a potential-drop signal which has the effect ofincreasing the capacitance exhibited by CRX to the extent thatoscillation of the oscillator is damped and quenched, even if sensorcapacitor C1 has not yet returned to maximum value. THus the oscillationceases and the amplifier output signal to the respirator unit decays tosubstantially zero volts value. If the respirator has not responded,decay of the amplifier output signal and consequent decay of the quenchsignal permits immediate resumption of oscillation if subatmosphericpressure prevails in the nose mask on the patient. Repetition of theoscillation-signaling cycle within a few milliseconds is of nosignificance if the respirator is proceeding through a cycle but has notyet produced superambient pressure on the upper surface of the sensordiaphragm 20, since the latching relay in the respirator has previouslybeen pulled in and is holding. If for some reason the respirator failedto respond to the initial amplifier output signal, a new oscillation ispromptly initiated and a repetitive signal transmitted to therespirator. Thus operation of the respirator is insured.

To prevent operation of the oscillator until the components have reachedthe desired constant operating temperature, a warmup timer circuit orunit 1410 is incorporated and is effective to maintain a highcapacitance value at CRX to bar oscillation in unit 40 for a determinedperiod of time sufficient for the oscillator to becometemperature-stable. Unit 140 comprises a transistor Q4, capacitor C8 andresistor R8. When the power circuit is closed as by switch S to energizethe system, Q4 immediately conducts, current flowing from lead P1 via aselected portion of a variable resistor R9, through 04 to ground. Thuspotential is supplied via resistor R7 and choke L2 to voltage-sensitivecapacitor CRX, raising that capacitance to a level sufficient to preventoscillation of the oscillator of unit 40. After a time determined by thevalues of R8 and C8, transistor O4 is biased off by the potential of thecharge accumulating on C8, the capacitance of CRX falls to a valuepermitting oscillation to commence, and the system is ready to senseinspiratory effort of a patient and initiate respirator operation. Thevalues of C8 and R8 are selected such as to permit the heater of unit 60to bring the oscillator to the desired temperature within, for example,minutes. Levels at which CRX is caused to quench, or permit operationof, the oscillator of unit 40 are set by adjustment of the values ofvariable resistors R9 and R10 comprised in a sensitivity control unit150.

The nose mask used in conjunction with respirator unit 90 may be of atype now commercially available, or may be such as is disclosed in U.S.Pat. No. 1,206,045. Exemplary electronic components for the detailedcircuitry shown are as tabulated in table I at the conclusion of thisspecification.

The preceding description makes it evident that the capacitance changeat capacitor C 1 necessary to trigger the oscillator can be made verysmall by adjustment of the sensitivity unit, since that change can bevery much less than the opposite change at C1 that would be necessary toquench the oscillator, and quenching is brought about by a powerfulaction of voltage-sensitive capacitor CRX initiated by the quench pulseunit 110. Thus even the very feeble effort of a neonate to inhale whilesuffering hyaline membrane syndrome or other respiratory distress issufficient to initiate positive respirator action. Further, the systemis extremely stable and immune to effects of changing temperature of theambient. Also it is evident the negative-pressure level at which actionis initiated is adjustable by varying the resistor means of thesensitivity unit. The time period between successive oscillator signalsis regulatable by change of the feedback circuit component values suchas C6-R4 and R6-R5. The pressure differential at the diaphragm 22.required to change the capacitance of C1 sufficiently to initiateoscillation can, by virtue of the adjustability ofthe sensitivitycontrol unit 150, be varied over wide limits e.g., from 0.l mm. to 5.0cm. water column. Thus the system is of value not alone in initiatingrespiration aid in response to extremely feeble respiratory efforts, butalso in promoting increasing effort on the part of the patient tobreathe voluntarily. The latter promotion is effected by graduallyincreasing the inspiratory effort necessary to initiate oscillation ofthe oscillator, by gradually reducing the sensitivity of the system.

TABLE I 1-5 pfd. R1 [00 K ohms C2 1.5-12 pfd. R2 220 ohms C3 22 pfd. R32.7 K ohms C4 3 pfd. R4 100 K ohms C5 0.02 mfd. R5 680 ohms C6 0.02 mfd.R6 2.7 K ohms C7 10 pfd. R7 2.7 K ohms C8 50 mfd. R8 2.2 megohms R9 2.5K ohms R10 l K ohms R11 22 K ohms Rx Klixon SST 1-2. C.

lN34 GE.

lN34 G.E.

CRX

MVl620 Motorola MPF l02, Motorola Q2 MPF 102, Motorola ()3 2Nl377,Motorola 04 MPF I02, Motorola l5 closed turns with tap at five turns022, 0.25" D. L2

22 microhenrics I claim:

1. A pressure-sensing signal generator system adapted to respond to verysmall difference between pressures exhibited at two closely spacedpoints and to produce an electric signal only immediately following suchresponse, said system comprising:

first means, including electronic oscillator means, efiective incidentto oscillation of the oscillator means to produce an output signalduring such oscillation;

second means, including pressure-sensitive capacitor means connected tosaid oscillator means and effective to inhibit oscillation of theoscillator means during absence of pres sure difference between twopoints therein and effective incident to establishment of a pressuredifference between said points to promote oscillation of said oscillatormeans; and

third means, including feedback means connected to receive an outputsignal from said first means, said third means effective upon receipt ofa. signal from said first means to quench oscillation of said oscillatormeans, whereby oscillation of said oscillator is quenched followingproduction of a signal representative of a pressure difference betweensaid two points, irrespective of continuation of the pressure differencebetween said two points.

2. A system as defined in claim 1, in which said third means comprisespotential-sensitive capacitor means shunting said first-named capacitormeans, and means rendered active by said output signal to apply voltageto said potential-sensitive capacitor means to increase the capacitanceexhibited by the shunt combination of capacitor means to effectquenching of oscillation in said oscillator means.

3. A system as defined in claim 2, including adjustable means forapplying an adjustable continuous potential to said potential-sensitivecapacitor means, whereby sensitivity of said system to pressuredifferential between said two points may be adjusted.

with respect to variables induced by temperature change.

5. A system as defined in claim 1, including respirator means connectedto receive an output signal produced by said first means and effectivein response thereto to proceed through a cycle of operation.

1. A pressure-sensing signal generator system adapted to respond to verysmall difference between pressures exhibited at two closely spacedpoints and to produce an electric signal only immediately following suchresponse, said system comprising: first means, including elecTronicoscillator means, effective incident to oscillation of the oscillatormeans to produce an output signal during such oscillation; second means,including pressure-sensitive capacitor means connected to saidoscillator means and effective to inhibit oscillation of the oscillatormeans during absence of pressure difference between two points thereinand effective incident to establishment of a pressure difference betweensaid points to promote oscillation of said oscillator means; and thirdmeans, including feedback means connected to receive an output signalfrom said first means, said third means effective upon receipt of asignal from said first means to quench oscillation of said oscillatormeans, whereby oscillation of said oscillator is quenched followingproduction of a signal representative of a pressure difference betweensaid two points, irrespective of continuation of the pressure differencebetween said two points.
 2. A system as defined in claim 1, in whichsaid third means comprises potential-sensitive capacitor means shuntingsaid first-named capacitor means, and means rendered active by saidoutput signal to apply voltage to said potential-sensitive capacitormeans to increase the capacitance exhibited by the shunt combination ofcapacitor means to effect quenching of oscillation in said oscillatormeans.
 3. A system as defined in claim 2, including adjustable means forapplying an adjustable continuous potential to said potential-sensitivecapacitor means, whereby sensitivity of said system to pressuredifferential between said two points may be adjusted.
 4. A system addefined in claim 1, including means for maintaining at least an activeelement of said oscillator means at superambient temperature, and meansfor inhibiting oscillation of said oscillator means pending attainmentof said superambient temperature, whereby said system is inhibited fromproducing an output signal until said oscillator means is stable withrespect to variables induced by temperature change.
 5. A system asdefined in claim 1, including respirator means connected to receive anoutput signal produced by said first means and effective in responsethereto to proceed through a cycle of operation.